The present invention relates to a silver halide emulsion, a preparation method of the silver halide emulsion and a silver halide photographic material by use of the silver halide emulsion.
Silver halide photographic materials (hereinafter, also referred to as photographic materials) are said to be a mature product having extremely high completeness. On the other hand, various enhanced performance is still required, such as enhanced sensitivity, superior image quality and minimized variation in performance after storage. Further, enhancement of suitability for rapid access by accelerating progression of development is also required and required levels thereof recently have become higher. Specifically with regard to enhancement of sensitivity, to maintain superiority of silver halide photographic materials over recent technical progress of digital cameras, further enhanced sensitivity compatible with storage stability is desired, while fogging is maintained at low levels.
To achieve further enhanced sensitivity and superior image quality, a technique for enhancing the ratio of sensitivity/grain size per silver halide grain has been explored in silver halide emulsions (hereinafter, also referred to as emulsions). As is commonly known, silver halide grains contained in a silver halide emulsion have various grain shapes, such as cubic, octahedral, or tetradecahedral, regular crystal silver halide grains, tabular silver halide grains having a single twin plane or plural parallel twin planes, and tetrapod-like or needle-like silver halide grains having non-parallel twin planes. Specifically, tabular silver halide grains (hereinafter, also referred to as tabular grains) are supposed to have the following advantages of photographic performance.
1. The ratio of grain surface area to grain volume (hereinafter, denoted as specific surface area) is relatively large, thereby causing a relatively large amount of a sensitizing dye to be adsorbed onto the grain surface, leading to enhanced spectral sensitivity relative to inherent sensitivity.
2. When tabular grain emulsion is coated and dried, tabular grains are arranged parallel to the surface of the support, thereby reducing the coating layer thickness and leading to enhanced sharpness of the photographic material.
3. Light scattering by silver halide grains is reduced, resulting in images having enhanced resolution.
4. Sensitivity to blue light (inherent sensitivity) is relatively low, so that in cases where a green-sensitive layer or red-sensitive layer is concurrently included, the density of a yellow filter layer can be decreased or the yellow filter can be removed from the photographic material.
5. A given level of sensitivity can be achieved by a low silver coverage relative to conventional grains, resulting in an enhanced sensitivity/graininess ratio and superior resistance to natural radiation.
Prior arts concerning tabular grains, specifically concerning manufacturing methods and techniques for usage thereof are described in, for example, U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4433,048, 4,414,306, 4,459,353; JP-B No. 4-36347, 5-16015, 6-44132 (hereinafter, the term, JP-B refers to published Japanese Patent); JP-A No. 6-43605, 6-43606, 6-214331, 6-222488, 6-230493 and 6-258745 (hereinafter, the term, JP-A refers to unexamined, published Japanese Patent Application).
To effectuate the foregoing advantages of the tabular grains, it is effective to employ tabular grains having relatively high aspect ratio. As is known in the art, increasing the iodide content makes it more difficult to prepare tabular grains having a high aspect ratio, so that most of tabular grains prepared by the foregoing prior arts were silver bromide or relatively low iodide silver iodobromide. However, low iodide silver halide grains exhibit relatively high development activity, and in addition thereto, high aspect ratio tabular grains further promote development, due to their grain shape factors. As a result, deterioration in graininess or influence by natural radiation easily occurs, making it difficult for tabular grains having a relative high aspect ratio to effectuate their inherent advantages. Further, tabular grains having a relatively high aspect ratio tend to increase fluctuation in grain size, making it difficult to optimize chemical sensitization or spectral sensitization and resulting in reduction in contrast or color density.
JP-A No. 6-230491 discloses tabular grains having an iodide content in the fringe portions of 1.5 to 50 times that in the central portion of the grain and an aspect ratio of 8 to 100. In this technique, however, allowing a high iodide phase to be arranged in the fringe portions led to lowering suitability for chemical sensitization, resulting in reduction in sensitivity and contrast. JP-A No. 6-235988 discloses tabular grains having a multiple structure comprising an inner shell, an intermediate shell containing relative high iodide and an outermost shell, having an aspect ratio of 3 to 100. However, it was proved that the relatively low iodide outermost shell external to the intermediate shell accounted for a relatively high fraction of the grain produced problems such that accelerated development due to tabular grains having a high aspect ratio caused deteriorated graininess. In view of the foregoing, advantages achievable by tabular grains having a relatively high aspect ratio could not be effectuated.
In general, tabular grains are formed by a process comprising the stages of nucleation, ripening and growth. It is substantially infeasible to selectively form tabular nucleus grains alone in the nucleation stage, so that grains other than tabular nucleus grains need to be allowed to disappear in the ripening stage. Thus, the nucleation and ripening stages largely affect grain size homogeneity or aspect ratio of the tabular grains.
JP-A No. 6-230491 and 6-230493 describe a preparation method of tabular grains having a relatively high aspect ration, with attention given in the nucleation stage, in which low molecular weight gelatin is used in the nucleation stage, and nucleation time xe2x80x9ctxe2x80x9d (sec) and temperature xe2x80x9cTxe2x80x9d (xc2x0 C.) within the reaction vessel at the nucleation stage satisfy the following relationship: 1 less than t less than xe2x88x92T+90. In this disclosure, however, although the nucleation temperature is defined as 20 to 60xc2x0 C., and preferably 30 to 60xc2x0 C., nothing is taught therein with respect to nucleation at lower temperature of less than 20xc2x0 C.
As disclosed in JP-A Nos. 63-11928, 1-131541, 2-838 and 2-28638, it is commonly known that the use of silver halide solvents such as ammonia and thioethers in the ripening stage enhances monodispersibility of tabular grains. Although this technique is effective for preparation of tabular grains having a relatively low aspect ratio, the use of such silver halide solvents increases the thickness of tabular nucleus grains so that this technique is taught not to be applicable in the preparation of relatively high aspect ratio tabular grains. In cases when silver halide solvents are not used in the ripening stage, it becomes difficult to allow twinned nuclei having non-parallel twin planes to be disappeared. As a result, it was proved that in a silver halide emulsion obtained by the foregoing technique were concurrently present high aspect ratio-having tabular grains and non-parallel-twinned crystal grains, leading to increased fogging and deteriorated graininess caused by such non-parallel-twinned crystal grains. Accordingly, technical development is urgently desired.
In view of the foregoing problems, the present invention was achieved. Thus, it is an object of the invention to provide a silver halide emulsion exhibiting enhanced relationship between sensitivity and fog density, a superior graininess, improved radiation resistance and improvements in contrast and color forming property, and silver halide photographic material by use of the emulsion. In addition thereto, it is an object of the invention to provide a preparation method of a tabular silver halide grain emulsion having a relatively high aspect ratio.
The above objects can be accomplished by the following constitutions:
A silver halide emulsion comprising a dispersing medium and tabular silver halide grains having an average overall iodide content of 3 to 15 mol % and comprising silver halide phases, at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12, wherein
a first of the silver halide phases is an internal phase (A) having an average iodide content of not more than 3 mol % and accounting for 50 to 85% of total silver,
a second of the silver halide phases is a phase (B) locating outside the phase (A), having an average iodide content of 8 to 25 mol % and accounting for 10 to 35% of total silver, and
a third of the silver phases is an outermost phase having an average iodide content of not more than 4 mol % and accounting for 0.5 to 15% of total silver.
Preferred Embodiments of the Invention are as Follows
1. a silver halide emulsion, wherein the silver halide emulsion comprises a dispersing medium and tabular silver halide grains having an average iodide content of 3 to 15 mol %; the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined below; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 12;
a phase (A) having an average iodide content of not more than 3 mol % and accounting for 50 to 85% of total silver,
a phase (B) having an average iodide content of 8 to 25 mol % and accounting for 10 to 35% of total silver, and
an outermost phase having an average iodide content of not more than 4 mol % and accounting for 0.5 to 15% of total silver;
2. a silver halide emulsion, wherein the silver halide emulsion comprises a dispersing medium and tabular silver halide grains, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; at least 50% by number of the silver halide grains exhibiting an adjacent edge ratio of 0.5 to 2.0; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 12;
3. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, the tabular silver halide grains comprising a phase (A), phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; at least 50% by number of the silver halide grains having at least 5 dislocation lines in edge portions of the grain; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 12;
4. a silver halide emulsion, wherein the silver halide emulsion comprises a dispersing medium and tabular silver halide grains, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; a ratio of a grain thickness to a thickness of the phase (B) in the section vertical to a major face being less than 5; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12;
5. a silver halide emulsion, wherein the silver halide emulsion comprises a dispersing medium and tabular silver halide grains having an average surface iodide content of 6 to 14 mol %, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; the tabular silver halide grains having an average spacing between twin planes of not more than 0.01 xcexcm; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12;
6. a silver halide emulsion, wherein the silver halide emulsion comprises a dispersing medium and tabular silver halide grains, said tabular silver halide grains comprising phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; the tabular silver halide grains having an average iodide content in the vicinity of corners, which is lower than an average surface iodide content; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12;
7. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; at least 50% by number of the tabular grains having dislocation lines in the peripheral region of major faces and the region surrounded by the dislocation lines being in a circular form; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12;
8. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, the tabular silver halide grains being formed in the presence of a compound having a group capable of releasing an iodide ion and represented by the following formula (I); and at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 12:
Formula (I)
{Xxe2x88x92(L1)n1}n2xe2x88x92L2xe2x88x92(SOL)m
wherein X represents an iodine atom; L1 and L2 each represent a bivalent linkage group; SOL represents an aqueous solubility-enhancing group; n1 is 0 or 1; m and n2 are each an integer of 1 to 4;
9. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; the tabular silver halide grains being formed in the presence of a compound having a group capable of releasing an iodide ion and represented by the formula (I) defined above; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 12;
10. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, said tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; at least one of the phase (A), phase (B) and outermost phase containing a compound represented by the formula (II); and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12:
formula (II)
[ML6]n
wherein M represents a filled frontier orbital polyvalent metal ion; L6 represents six coordinated complex ligands; and n represents -, 2-, 3- or 4-;
11. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, having been prepared by a process comprising a nucleation step, ripening step and growth step; an average iodide content of tabular grains in the nucleation step being not more than 2 mol % and an average iodide content of the prepared emulsion being 5 to 12 mol %; and at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12;
12. a silver halide emulsion, wherein the silver halide emulsion comprises tabular silver halide grains and a dispersing medium, said tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above; at least 50% of the total projected area of the tabular silver halide grains being accounted for by grains having an aspect ratio of not less than 12; at least 10% by weight of the dispersing medium is a chemically modified gelatin;
13. the silver halide emulsion of any one of 1 through 12, wherein at least 50% of the total projected area of the tabular silver halide grains being accounted for by tabular grains having an aspect ratio of not less than 15;
14. the silver halide emulsion of any one of 1 through 13, wherein a coefficient of variation of grain size of tabular silver halide grains contained in the silver halide emulsion is not more than 25%;
15. the silver halide emulsion of any one of 1 through 14, wherein tabular silver halide grains contained in the silver halide emulsion substantially are silver iodobromide;
16. the silver halide emulsion of any one of 1 through 15, wherein concentration of the silver halide emulsion is performed by means of ultrafiltration during at least a part of the growth step of silver halide grains;
17. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a pBr of 1.8 to 2.8, a pH of 1.5 to 3.0 and a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having an average molecular weight of not more than 30,000;
18. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having an average molecular weight of not more than 30,000 and at least a part of the ripening being performed in the presence of a silver halide solvent;
19. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having an average molecular weight of not more than 30,000 and at least a part of the ripening being performed at a pH of 7 to 12;
20. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having an average molecular weight of not more than 30,000 and at least a part of the ripening and growth is performed at a relatively high temperature having a difference of 40 to 70xc2x0 C. from the nucleation;
21. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having an average molecular weight of not more than 30,000, the silver concentration of a reaction solution being 1xc3x9710xe2x88x923 to 1xc3x9710xe2x88x922 mol/l at the time the nucleation is completed;
22. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the tabular silver halide grains comprising a phase (A), a phase (B) outside the phase (A) and an outermost phase within the grain, as defined above, the method comprising the step of preparing the emulsion by the use of a seed grain emulsion, wherein the silver concentration of an aqueous solution containing the seed grain emulsion in a reaction vessel is 1xc3x9710xe2x88x923 to 1xc3x9710xe2x88x922 mol/l before starting a grain growth step;
23. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the method comprising the steps of nucleation, ripening and growth, wherein the nucleation is performed at a temperature of 5 to 20xc2x0 C. in the presence of a low molecular weight gelatin having a mean molecular weight of not more than 30,000, and at least a part of the growth being performed in the presence of the compound represented by formula (I) defined above;
24. a preparation method of a silver halide emulsion, wherein at least 50% of the total grain projected area is accounted for by tabular grains having an aspect ratio of not less than 12, the tabular silver halide grains comprising the phase (A) within the grain, as defined above and phase (B) defined above being formed outside the phase (A) so that an average aspect ratio after completion of grain formation is smaller than an average aspect ratio after completion of phase (A) formation;
25. the preparation method of a silver halide emulsion of any one of 17 through 24, wherein concentration of the silver halide emulsion is performed by means of ultrafiltration;
26. a silver halide photographic light-sensitive material comprising on one side of a support at least a light-sensitive layer, characterized in that the light-sensitive layer comprises a silver halide emulsion of any one of claims 1 through 16; and
27. a silver halide photographic light-sensitive material comprising on one side of a support at least a light-sensitive layer, characterized in that the light-sensitive layer comprises a silver halide emulsion prepared according to the method of any one of claims 17 through 25.